Opinions/Guidance on Three Jaw Chucks

[Mtndew]

"Semi steel" chucks have been around for 100 years. Common in 4 jaws.

Yeah I forgot about that.

 

[jbacc]

Sounds like jaws may be in horrible shape. Maybe you can work on the a little and get better results. Take the thing apart and clean the scroll. It may be full of ancient crap.

Thanks, I already took it apart and meticulously cleaned everything. I also stoned all the surfaces including the back plate and again cleaned everything. I did initially find that two of the top jaws were bolted to the wrong master jaws and I thought that most certainly was my problem, but alas, it was not.

Thanks again,

Joe

 

[AlfaGTA]

I have a different perspective to this question.
First off, I don’t place any premium on having a “set true” chuck.
A good quality steel body chuck that is direct or has a mounting plate.

It it’s a matter of your work approach.
If starting with raw stock to make your part, if your process is properly laid out and executed the , if any, runout is a non factor.
It’s important that the jaw faces are parallel , so that the part is gripped full length of the jaw.
I was taught , when using a 3 jaw to finish the part in a single chucking if possible, even at the expense of overall speed.

If a recheck is required to finish the part , a better holding system should be considered.
Collets, soft jaws or a 4 jaw are just better , more repeatable
Shaft work should be finished between centers if possible.
Any 3 jaw you purchase, will almost immediately begin to degrade with any use, the trick is to not depend on it being accurate as to overall runout.
My
Primary lathe at work is fitted with a Shunk Rota G manual 250mm chuck. $7000+ , not offered as an “adjust true”.
Not a scroll chuck but rather a sliding plate setup ( more accurate , constant geometry) I still work with the idea of finishing in a single chucking. (Exception of part of facing)I use soft jaws when doing multiple repeat parts.
Cheers Ross

 

[jbacc]

I have a different perspective to this question.
First off, I don’t place any premium on having a “set true” chuck.
A good quality steel body chuck that is direct or has a mounting plate.

It it’s a matter of your work approach.
If starting with raw stock to make your part, if your process is properly laid out and executed the , if any, runout is a non factor.
It’s important that the jaw faces are parallel , so that the part is gripped full length of the jaw.
I was taught , when using a 3 jaw to finish the part in a single chucking if possible, even at the expense of overall speed.

If a recheck is required to finish the part , a better holding system should be considered.
Collets, soft jaws or a 4 jaw are just better , more repeatable
Shaft work should be finished between centers if possible.
Any 3 jaw you purchase, will almost immediately begin to degrade with any use, the trick is to not depend on it being accurate as to overall runout.
My
Primary lathe at work is fitted with a Shunk Rota G manual 250mm chuck. $7000+ , not offered as an “adjust true”.
Not a scroll chuck but rather a sliding plate setup ( more accurate , constant geometry) I still work with the idea of finishing in a single chucking. (Exception of part of facing)I use soft jaws when doing multiple repeat parts.
Cheers Ross

Thanks for sharing your perspective, Ross, I do appreciate it.

Joe

 

[guythatbrews]

Say what you will, but a set-true type chuck is pretty handy.

Collets don't work if you don't have the correct size and don't want to bore an emergency collet for just a few parts. And they might be very close but not always close enough.

By all means do all you can in one operation chucking on stock. Then It's nice to be able to flip that odd sized (or to-big-for-collet) part around, indicate in .001 or .002, and complete the second side. Sure, a four jaw would work and hold better. but why change chucks if you don't have to?

 

[AlfaGTA]

Sure, a four jaw would work and hold better. but why change chucks if you don't have to?

Start with the 4 jaw if you know you are going to have to flip the part. No change needed.
Cheers Ross

 

[eKretz]

Yeah, I'll take a Set-Tru any day. Sometimes saves needing to swap a chuck for a quickie job and that's enough for me. Plus then the relevance of a worn scroll is basically nil as long as the chuck repeats once set. If it doesn't, then it needs rebuilt or replaced. Although soft jaws solves that problem pretty handily too.

But yeah a 4-jaw is basically the solution to any of this. But it sure is nice having a scroll chuck for multiples with lots of setups.

 

[MCritchley]

Current ones I believe are made in Slovakia (?) and marked Pratt Burnerd America. I have one and it's very nice and quite accurate. I think the one I linked to was made before that era as it is still marked Pratt Burnerd International.

PBA’s are not what they were 15 years ago when I bought one for my 10EE, that was the best chuck I’ve used, no more.
I just sent back a Chuck to PBA, poor quality. I put PBA in the same bucket as Kalamazoo.
I went to Buck and am very happy. My second choice is Bison, they are good I’ve bought several and haven’t had an issue.

The Bucks are just a bit better and smooth IMO.

 

[jbacc]

I bit the bullet and ordered a new Bison Set-Tru Chuck. It made the most sense because as was suggested, I can reuse my current back plate which saves me a fair amount of money.

I thank you all for taking the time to share your thoughts and help guide me in the right direction, I truly appreciate it.

Joe

 

[farmersamm]

Not to start a fight............but I see these threads all the time.

"Woe is me..........my 3 jaw has runout". IT'S A 3 JAW! (LOL)

Frankly................what's the problem??

Put some stock in it, turn it, and just make sure that you do everything that needs done to that stock before ya take it out. It ain't a 4 jaw, and never will be a 4 jaw.

The machine axis is true, despite the 3 jaw runout. You'll still get a perfect part, as long as you don't take it out of the chuck, and expect to put it back again and hit dead 0.

Think of it in terms of Ding Dongs.............................. You go to the convenience store and buy a package of Ding Dongs. You go to the fancy Yuppie bakery to buy a baguette. A 3 jaw is the convenience store of chucks.

 

[EmGo]

"Woe is me..........my 3 jaw has runout". IT'S A 3 JAW! (LOL)

Wasn't going to go here because telling people their machining practices are ... errr ... possibly less than ideal doesn't make one any friends. But yeah, have to agree with both of you above, the fixation over runout in a three jaw is very youtubey. Do it all in one chucking is what I learned fifty years ago and no, I ain't gonna learn to snivel about it being the chuck's fault when it's my own lack of skill That's not further eddication, that's just dumb.

If it needs to flip and remain concentric, use a collet. Or a four-jaw (ick) or some sort of set-tru system. Doing gear blanks in production in an engine lathe, which I bet is not real common anymore, I learned to love a 6-jaw buck. But did all of one side at a time then indicated the other and did not expect the chuck to do the work and even thought about which face and indicating area was perpendicular to the bore for later processing.

I've seen a few youtubes with people whining about "low quality" chucks because they don't repeat within a half. That's just dumb. They aren't supposed to.

 

[jbacc]

I don’t take any of the opinions and/or advice as a negative, in fact, I appreciate people sharing them.

My machinist skills are suspect at best, I’m a garage hack who enjoys working with tools and machinery.

I completely understand and accept the limitations/tolerances of a three jaw chuck. This particular chuck in question is a 6” Bison Set-Tru. Like all my three jaw chucks, I use it for convenience and accept the variations in accuracy within their stated tolerance but this chuck was the most inconsistent I have ever used.

After dialing in a part using the Set-Tru feature, like any three jaw chuck, if the machining was done in one operation, all was well. However, if you removed the part and placed the very same part back into the chuck, it would not repeat by several thousandths or more and a part of a different diameter was ridiculously off.

These inconsistencies defeated the purpose and convenience of using a three jaw chuck so I decided that for me, replacement was the best course of action.

I have grinded the jaws on other chucks with varying degrees of success but this chucks issues seem to indicate there was a lot of wear on the internal parts that would not have been corrected by grinding the jaws.

Again, I understand the limitations and tolerances of a three jaw chuck and this one fell way outside those tolerances and would not repeat on any diameter size.

I was hoping to save a little money by possibly trying one of the lesser quality imports but in the end, I was not willing to take the chance. So, I bit the bullet and purchased a brand new Bison Set-Tru and reused my current back plate.

All the issues I was experiencing with the worn out chuck are gone so in my specific situation, the new chuck was well worth the expense for the type of work I do and I am pleased with my new chuck and my decision to purchase it.

Thanks to all for sharing your thoughts, advice and sentiments. I learn from all of them.

Joe

 

[Ox]

It is threads like this that my peers piss me off the worst.

Everyone is the first to bitch about imports taking everything over (especially in the market that they serve) but when they are sourcing an item, they are all about the cheapest, or at least cheap-er.

And this is why the old name brand chucks are done, and their name stamped on some import unit.

I am not sure what Buck's story is currently?
I believe that Hardinge owns them, but I don't recall where they are making them?

But one that I know for sure - is Kalamazoo (Michigan) Chuck Company.
They doo import some as well as y'all are all about cheap, but they also offer Made in USA chucks as well.
They started as Made in USA and added the imports along the way.

KCM offers US Made Chucks from our Michigan factory

KCM is your American source for standard and custom workholding equipment. We make and service heritage Buck Chuck designs. We offer engineering support for your technical questions and customer service from our Michigan factory.

www.kzoochuck.com

I have several of them. 10" through 15" I think.
3 and 6 jaws.

These chucks only offer 1 pinion in most cases. This pisses me off most of the time, but that IS what will get you the best repeatability, so I git it.


-----------------------------

I am Ox and I approve this post!

 

[implmex]

Good morning All:
When the problem is as the OP describes:
"After dialing it in on a specific diameter part, it will not repeat on the same part and is off by several thousandths or more."

I've found a common problem with old beater chucks is that the scroll has too much clearance on its post, and will move around when you tighten the chuck.
If you cannot grip the same piece consistently over and over within around 0.0005" of TIR after you've dialed it in once with the Set-Tru screws and using the same pinion over and over, that's the diagnosis I am most suspicious of.

A good way to check, is to snug up a piece of round stock but do not tighten the jaws hard.
Mark the pinion you used and dial in your part.
Now reef a bit more on each pinion in turn and see what it does to the runout.
The pinion that's in use will push the scroll away from it, because it's a bevel gear set, so the forces on the gear teeth want to push the gears apart.
If the runout is worse after you snug the jaws a bit more...that's the likely culprit.

Next in line is worn jaw slots that allow the jaws to cant sideways or rock, and lowest on the list is a worn scroll.
I say this because if the scroll always rotates back to the same point when you clamp your workpiece and if you've already dialed it in once, then only changes in either the scroll's position within the chuck body or changes in the jaws positions within the chuck body can account for the inconsistency you see.
This remains true regardless of whether the clamping faces of the jaws are perfect, whether the pinions are worn, or whether the scroll is worn. (Unless, of course, your stock's not round)

So I'd pull the chuck apart and see how much clearance there is between the bore in the scroll and the post on which it rides.
Fixing either is not trivial, but it is possible with enough patience.
Next I'd check the jaw slots for clearance with the jaws...a thou or two will not make much difference but more than that will.

Last point...the whole idea of a Set-Tru chuck is that you adjust out the runout with every clamping, so you can get it within tenths without much effort.
So even if the chuck is not ideal, I'd live with it unless you have such a boner for a new one that you're willing to drop the coin.

Only you (our OP) can decide how big your hard-on actually is.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[jbacc]

Good morning All:
When the problem is as the OP describes:
"After dialing it in on a specific diameter part, it will not repeat on the same part and is off by several thousandths or more."

I've found a common problem with old beater chucks is that the scroll has too much clearance on its post, and will move around when you tighten the chuck.
If you cannot grip the same piece consistently over and over within around 0.0005" of TIR after you've dialed it in once with the Set-Tru screws and using the same pinion over and over, that's the diagnosis I am most suspicious of.
Next in line is worn jaw slots that allow the jaws to cant sideways or rock, and lowest on the list is a worn scroll.
I say this because if the scroll always rotates back to the same point when you clamp your workpiece and if you've already dialed it in once, then only changes in either the scroll's position within the chuck body or changes in the jaws positions within the chuck body can account for the inconsistency you see.
This remains true regardless of whether the clamping faces of the jaws are perfect, whether the pinions are worn, or whether the scroll is worn.

So I'd pull the chuck apart and see how much clearance there is between the bore in the scroll and the post on which it rides.
Fixing either is not trivial, but it is possible with enough patience.
Next I'd check the jaw slots for clearance with the jaws...a thou or two will not make much difference but more than that will.

Last point...the whole idea of a Set-Tru chuck is that you adjust out the runout with every clamping, so you can get it within tenths without much effort.
So even if the chuck is not ideal, I'd live with it unless you have such a boner for a new one that you're willing to drop the coin.

Only you (our OP) can decide how big your hard-on actually is.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

Most of the fixes you described for beater chucks is beyond my skill level. As far as Set-Tru chucks, yes, the main purpose is to have the ability to adjust each part within a few tenths. However, as with all my adjustable chucks that are in good condition, I can adjust the chuck to a point that it is within the stated tolerance for any diameter part I clamp and that is important to me. So, I guess in your words, my hard-on was large enough for me to pay the extra coin for a chuck that suits my needs. Your mileage may vary but replacing the chuck was what worked best for me.

Cheers.

 

[implmex]

Hi again jbacc:
I'm pleased you found a solution you are happy with...that's obviously the most important thing, and since you are doing this for pleasure, your purchase is fully justified, if your pleasure is increased by using a fine tool and enjoying what it can do for you.
All is right with the world!

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[EmGo]

Everyone is the first to bitch about imports taking everything over (especially in the market that they serve) but when they are sourcing an item, they are all about the cheapest, or at least cheap-er.

And this is why the old name brand chucks are done, and their name stamped on some import unit.

See, your kalamazoo chuck would be wasted on me because from the very first time I was taught to use a lathe, I was taught to never even try that stuff. And this was all before there were any imports, with who knows what brands (tho I am pretty sure the six-jaws were Buck) because we would never even consider just turning a part around and expecting the chuck to be perfect.

I don't have the beginnings of a clue what the runout was on any three jaw I've ever owned

Now collets you expect to run concentric, but a three-jaw ? No way jose.

 

[implmex]

Hi EmGo:
Yeah, you make a good point, but for one small quibble.
Even collets are not perfect...you just need to use a more sensitive dial indicator to find the flaws.
My Lyndex collets can hold maybe a tenth or two...plenty good for turning but rougher than guts for grinding.
If runout as good as your spindle bearings is the goal, then I, just like you, will move heaven and earth to put in all my features that must be concentric in one chucking.
Even grinding between centers takes on a whole new requirement for attention to detail when your runout goal is under 50 millionths, as I'm sure you know as well as I.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com

 

[EmGo]

My Lyndex collets can hold maybe a tenth or two...plenty good for turning but rougher than guts for grinding.

I don't think I've ever ground anything in a collet ... between-centers guy here. But I can actually see my parts without one of those funky enlarging visors

 

[implmex]

Hi again EmGo:
You wrote:
"But I can actually see my parts without one of those funky enlarging visors"

That makes you a better man than me...I'm blind as a bat, and it ain't gettin' any better as I decline into dribbling senescence.
You lucky bastard you!

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com